The invention relates fo an electronic fuel injection control device for an internal combustion engine and, particularly, to a fuel injection control device comprising an electronic circuit requiring a power source of fixed voltage.
A fuel injection control device for an internal combustion engine carries out calculations based on various detecting signals indicating the condition of the engine. Such detecting signals are, for example, an air flow signal indicating the amount of air which is introduced into the engine and an engine speed signal indicating the number of revolutions per minute of the engine. After carrying out the calculations, the control device controls the opening time of fuel injection valves for supplying fuel to the cylinders of the engine.
The conventional control devices of the above described kind are divided into two types. One of which is an analogue type and the other of which is a digital type. Control devices of the digital type ordinarily comprise a digital electronic circuit including a microprocessor, a digital memory element and the like. The digital electronic circuit requires a 5-volts d.c. power source of fixed voltage for its operation.
An automobile battery is ordinarily used as the power source for the electronic circuit of the fuel injection control device which controls injection amount of the fuel supplied to an automobile internal combustion engine. However, the terminal voltage of the automobile battery is greatly changed depending on the running condition of the engine. Especially, at the start of the operation of the engine, a large current is supplied to a starter motor of the engine and, therefore, the terminal voltage of the battery is greatly decreased. Furthermore, when the temperature of the outside air is low, or if the battery is degrated, the terminal voltage of the battery at the start of the operation of the engine is often lower than 5-volts.
Accordingly, in a conventional control device of this type, the occurrence of erroneous operations at the start of the operation of the engine has heretofore been prevented by elevating the battery voltage, adjusting the elevated voltage to a predetermined fixed voltage and feeding the fixed voltage to the electronic circuit, by using a d.c. to d.c. voltage converter (DC-DC converter). However, such a DC-DC converter is very expensive and its size is large. Accordingly, the loading an automobile with the DC-DC converter involves various problems, which have impeded utilization of a digital electronic fuel control device of an internal combustion engine for an automobile.